A modulator is arranged in a device for signal transmission, such as used in systems for wireless or wireline communication. One of the functions of a modulator is to modulate a useful signal representing an information to be transmitted onto a carrier frequency signal so to provide a transmission signal. The transmission signal is amplified before being provided to a transmission channel. In case of a base-station of a mobile communication system, the amplifier has to provide for a high amplification gain.
Generally, in mobile communication systems, diverse modulation schemes allowing for a high bandwidth are provided, such as EDGE (Enhanced Data Rates for GSM Evolution), UMTS (Universal Mobile Telecommunication System), etc. These modulation schemes usually provide a non-constant envelope of the transmission signal. This may be due to an amplitude modulation of the transmission signal. The amplitude modulation carries part of the information transmitted. To allow for a correct demodulation and reassembly of the information, certain linearity requirements have to be fulfilled by the modulator. E.g., the linearity requirements are set by a standard specification. In consequence, the power amplifier of a base-station has to provide a linear amplification over a wide range of signal level. This is usually achieved by providing for a “quasi-linear” amplifier running with a high back-off to ascertain the linearity requirements with respect to the transmission signal. This mode of operation leads to a low efficiency in power and usually to higher costs in production of an according modulator.
For these and other reasons, there is a need for the present invention.